1. Field of the Invention
The present invention relates to a release (coated) film which has an anchor layer and a release layer in this order on at least one surface of a film substrate. Specifically, the present invention relates to a medical release film for, for example, applying an external medicine and a release film for a component of a display device such as PDP (Plasma Display Panel) and OLED (Organic Light Emitting Diode) display or a polarizing plate for LCD (Liquid Crystal Display).
2. Description of the Related Art
Conventionally, release films, which have a release layer on at least one surface of a film substrate, have been widely used as a ceramic green sheet, as release films of a tackiness label paper, a tackiness film, an LCD polarizing plate and a tackiness optical display component of a PDP or an OLED display, and as a medical release film for applying an external medicine. These release films have a release layer of silicone resin coated and formed on at least one surface of a plastic film.    <Patent document 1>: JP-A-H11-300897.    <Patent document 2>: JP-A-H9-156060.    <Patent document 3>: JP-A-H7-003215.
As display devices such as LCD tend to be larger in area and higher in resolution in recent years, higher quality appearance and higher capability of preventing defects caused by foreign materials are required in the display devices. In the case where the release film is applied to a tackiness polarizing plate or a protection film of an optical component such as retardation film, it is necessary for the release film to have no or few foreign materials. A foreign material on the optical component may cause an error in displaying an image.
Similarly, in the case where the release film is used together with a medical sheet for, for example, applying an external medicine, it is necessary to leave no or few foreign materials on the release film. In addition, in the case where the release film is stuck together with a tackiness layer of a tackiness label paper or tackiness film, it is also necessary to leave no or few foreign materials on the release film.
After the release layer is coated on a substrate and heated to cure, an inspection searching for a foreign material or a defect on the release film is performed as an in-line process or as an off-line process in such a way that inspection equipment analyzes a camera image or an inspector performs a visual check. Depending on the circumstances, the inspection might be performed after the release film is stuck to its main body.
In this inspection, mechanical problems sometimes occurred while the inspection equipment searched for a foreign material. In the case where the inspection is performed with human eyes, problems such as a decrease in efficiency etc. sometimes occurred due to the inspector's nauseousness and/or eyestrain.
In addition, in some types of release films, a print layer is arranged on the opposite surface of the (transparent) film substrate or between the film substrate and the release layer so as to provide the release film with the capability of showing a character, a message, a design and/or a decorative pattern etc. and a high design effect (including aesthetic appearance). Particularly in the case of a medical release film, the print layer tends to be arranged in order to display a drug name, application considerations, warnings, a trademark and/or a logo etc. In such a case, an unclear display and/or a faint image etc. as well as a poor design effect and/or ugly appearance sometimes occurred.
In addition, an anchor layer is arranged in the release film in order to improve adhesiveness between the film substrate and the release layer. The anchor layer provides long-term preservation stability to the release film after the release film is manufactured. In particular, in the case where the release film is used for medical application, it is preferable to form the anchor layer between the film substrate and the release layer in order to prevent the drug from degrading with time.
In the case of a release film in which the anchor layer is formed, however, it is sometimes still more difficult to perform the inspection searching for any foreign materials and defects than in the case of a release film in which the release layer is directly formed on the film substrate without arranging any anchor layer therebetween. In addition, in the case of the release film in which the anchor layer is formed, an image printed within the print layer sometimes appears still less vivid or unclear than in the case of the release film in which the release layer is directly formed on the film substrate without arranging any anchor layer therebetween when the print layer is formed.